Three weeks after watching a massive wave smash into the Fukushima nuclear plant, Hiroyuki Kohno is heading back to the disaster zone to join crews struggling to avert a meltdown.

The 44-year-old radiation controller, who has worked in the nuclear industry since his late teens, has taken on a job many others have declined, with a clear understanding that the mission will likely be the last of his career.

"To be honest, no one wants to go," Kohno, who is soft-spoken and bespectacled, told AFP at the evacuation centre in the city of Kazo north of Tokyo that has been his home since the March 11 disaster.

"Radiation levels at the plant are unbelievably high compared with normal conditions. I know that when I go this time, I will return with a body no longer capable of work at a nuclear plant."

Kohno, who was employed at the now-crippled Fukushima Daiichi plant for a decade, left northeastern Japan soon after the quake and tsunami, but a fortnight later he received an email he had been half expecting.

"Attention," read the email from his company, a subcontractor of plant operator Tokyo Electric Power Co. "We would like you to come work at the plant. Can you?"

Single and without a family of his own, he felt it was his duty to accept the assignment.

"The work rotation is becoming increasingly difficult, and my friends have families to return to," he said.

But Kohno is not just a company employee. He is also the eldest son in his family, and when he broke the news of his return to the plant to his parents, he did his utmost to downplay the risk.

They were not fooled. His father, who also worked many years as an electrical engineer at Fukushima Daiichi, told him to follow his heart. His mother's reaction was simpler: "Come back as soon as possible."

Kohno can only begin to imagine what conditions await him at Fukushima, but his recollections are vivid of the fateful day when the 9.0-magnitude earthquake struck.

He was in the turbine building of one of the reactors when suddenly a desk nearby began trembling.

At first he thought someone was playing a prank. Then he remembered there had been a small earthquake the day before, and assumed it was just an aftershock.

But when equipment around him began to shake and creak loudly, he realized this was different.

"It was a sound I'd never heard before in my life and I immediately thought, 'This time the quake is huge.'"

Unable to stand straight, he leant against the concrete wall, but it too was shaking violently.

Workers started pouring out of the building, skipping the normal radiation screenings and running up a nearby hill.

"We started hearing people screaming: 'Tsunami coming!' From the bay we saw white waves hurling towards us. I was terrified," he said.

He joined the exodus up the hill, watching as a wave swallowed a ten-meter pole and swept through the plant, leaving the six reactors looking like barren rocks in the middle of a roaring sea.

"My family was unscathed, but many of my friends lost loved ones," he said.

As the rest of Japan now seeks to move on from the nation's worst post-war disaster, workers at Fukushima are still struggling around the clock to contain the crisis.

The March 11 tsunami broke down the plant's cooling systems, provoking a series of explosions and fires, and causing radiation to leak into the air, soil and ocean.

Emergency work ranges from removing massive amounts of radioactive water to clearing contaminated rubble, measuring radiation levels and hooking up power cables to kick-start cooling.

Kohno said he will be assigned to the plant's headquarters located in a quake-resistant tower, where he will be exposed to the same amount of radiation every hour that ordinary people experience in a whole year.

He will be joining a team that has been lauded worldwide, with media affectionately dubbing the core unit the "Fukushima Fifty", but he said heroics were not his motivation.

"There's a Japanese expression: 'We eat from the same bowl.' These are friends I shared pain and laughter with. That's why I'm going," he said.

Out of about 50 technicians at his company, around ten are currently on site. A majority likely refused to go, he said.

"When I think about it I get nervous. I was quite anxious for the first four days after I said I would be going. I especially think about it at night," he said.

It is hard to completely forget the risks that await him - at least 19 workers so far have been injured due to high radiation levels.

His friends have also described terrible working conditions, amid constant exposure to the highly penetrating gamma-rays.

"Although they don't come out and say it openly, they all want to be replaced immediately," he said.

He expects to work without pause for several days before taking two or three days of rest. And like his workmates, he will probably get by on a diet of canned food and energy bars.

"We tell each other that Japan was utterly destroyed in World War II. Now Japan has once again been burnt to the ground. Although the battlefield is different, we are the modern-day kamikazes," he said.

"Kamikaze" refers to suicide pilots who flew planes filled with explosives into Allied ships at the end of the war, and in modern Japan the word carries connotations of sacrificing one's life when ordered to.

To be sure, times have changed. The US is no longer a mortal adversary but a valued friend, and Kohno does not expect to die. Even so, Kohno is awed at the task ahead.

"Our enemy is now different. But this time it is perhaps more terrifying," he said.